1.0.0-beta2

• added PhpRedisStore
• added CachedStore
• removed optional argument $cache from JsonFileStore::__construct()
• removed implementations that don't make sense for a key-value store:
  • MemcacheStore (not persistent)
  • MemcachedStore (not persistent)
  • SharedMemoryStore (not persistent)
• added Serializer utility
• KeyValueStore::get() now throws an exception if the value cannot be unserialized